Reforming is well known and performs a major function is the present-day petroleum refinery industry. It represents a convenient method for upgrading gasoline boiling range hydrocarbons having a relatively low octane number to aromatic enriched product having an octane rating in excess of 100. It is thus of economic importance and considerable energy has been expended to improve upon the reforming operation so that less critical charge material can be upgraded to a desired product with a minimum loss in volume of product available from the charge material. It is well recognized that in reforming a number of reactions occur and that each reaction can be particularly favored by adjustment of reaction conditions in cooperation with a particular composition. In naphtha reforming operations endothermic reactions predominate in the first stages of reforming while exothermic reactions increase and may even predominate in the later stages of the reforming operation. Furthermore, specific operating conditions are selected for use in conjunction with the particular catalyst and hydrocarbon charge employed. To take advantage of the reactions and reaction sequence in catalytic reforming it has been the practice to employ in combination a plurality of fixed bed reactors arranged in series with provision for adjusting the temperature essential by reheating of the hydrocarbon reactant between reactors. Generally, for a matter of economic convenience the pressure employed in each reactor is decreased in the direction of hydrocarbon flow sequentially through the plurality of reactors to avoid use of expensive compressors between the separate reactors. Thus the pressure drop will not be substantially more than that encountered by the reactants passing through the reactors, catalyst beds, heaters and inter-connecting piping to provide the desired flow of reactants therethrough. In addition the vapor inlet temperature selected for each reactor is dependent upon the charge stock composition, the hydrogen to hydrocarbon ratio employed, the reactant space velocity, the type and distribution of catalyst in the plurality of the reactors, the degree of conversion desired and product selectivity desired from the reactors. Catalytic reforming of hydrocarbons generally comprises four major reactions which can be adjusted in magnitude by reaction conditions and catalyst employed. The predominant reaction in the first stage of reforming is known to be dehydrogenation to convert naphthenes to aromatics. Another reaction essential in this stage is the isomerization of cyclopentanes to cyclohexanes. Other reactions which occur and are controllable to some extent are the cracking of naphthenes and paraffins and the isomerization of paraffins. The major reforming reaction which may occur in a subsequent stage is dehydrocyclization of straight chain paraffins to aromatics thereby further increasing the octane rating of the product material. In dehydrocyclization reactions, the paraffins are cyclized and dehydrogenated to form aromatics. To maximize product volume from a given charge material a closely controlled operation to optimize both platinum type hydrogenation-dehydrogenation and acidic catalyst functions is required. A third reaction of importance in reforming is concerned with the isomerization of paraffins, olefins, and naphthenes. The isomerization of paraffins, not cyclized results in significant octane improvement and requires an acid function. It is well known, however, that acid functions contribute to cracking and therefore hydrocracking of constituents in the hydrocarbon charge must be selectively controlled to avoid producing undesired gaseous components and carbonaceous material formation in the reforming operation. In the prior art practice of reforming naphthene charge material in the gasoline boiling range it has been found desirable to maintain a selective balance in the acidic and hydrogenation-dehydrogenation functions of the reforming catalyst so that the selectivity of the reforming operation can be related to the charge stock composition, operating conditions and reformate product desired.
In practice reforming catalysts of the prior art have particularly includes a platinum group metal selected from within relatively narrow limits of from about 0.15 percent to about 1.0 percent by weight of the catalyst. At these concentrations the active platinum sites may be spread throughout the support matrix and the activity level of the hydrogenation-dehydrogenation function can be controlled substantially as desired. In addition the catalyst acid function has been limited to maintain a desired balance with the hydrogenation-dehydrogenation function of the catalyst. Platinum type reforming catalysts have been modified by a great number of activating agents or promoters as a basis for improvement upon the selectivity of the reforming operation. However, because of inherent difficulties in operation and problems associated with improving upon catalyst life between regenerations, the industry will continue to search for methods for improving upon the already known reforming operation.